Sustainable Niger Seed Oil -Derived Polyurethane Coatings for Wood Protection: Development, Characterization, and Performance Analysis

The aim of this study is the development of a polyurethane (PU) wood surface coating formulated from a niger polyesteramide polyol derived from niger seed oil (NSO). The synthesis procedure began with the preparation of long-chain fatty diethanolamide through the amidation of niger seed oil, followed by esterification with isophthalic acid to obtain hydroxyl-functional polyesteramide polyols. Structural confirmation of the fatty amide and final bio-polyol was achieved using ATR-FTIR and 1H NMR spectroscopy, which verified the successful incorporation of both amide and ester groups. Subsequently, PU coatings were formulated using the synthesized polyol, which was reacted with two aliphatic/aromatic isocyanate systems, hexamethylene diisocyanate biuret (HDI) and methylene diphenyl diisocyanate (MDI), to produce bio-based polyurethanes. When applied to wood panel substrates, the coatings exhibited high gloss, strong adhesion, and notable resistance to chemical exposure. Additionally, the films demonstrated self-cleaning behavior and inhibited bacterial growth, which enhances their functional advantages for wood protection. Thermogravimetric analysis revealed good thermal stability up to 300 °C for both the coatings. And scanning electron microscopy confirmed that the coating had a homogeneous and defect-free structure. These results suggest that NSO-based niger polyesteramide polyol could serve as a renewable source for high-performance polyurethane wood coatings.